The present invention relates to a communication system, and more particularly to management of an antenna array.
Aircraft communications systems usually include a receiver-transmitter, a digital interface of the control panel mechanism to and from the receiver transmitter, and an antenna system. The antenna system of a typical communications system is connected to the receiver-transmitter by a coaxial cable, sometimes known as a transmission line. This basic arrangement can be found in aircraft and in ground installations.
Some conventional communications systems connect the receiver-transmitter and the antenna as a dedicated, matched pair, and the antenna is tuned to operate efficiently over the particular receiver-transmitter's operating range. In more complex applications, a receiver-transmitter may be connected to a second antenna by a control mechanism and a coaxial relay. A typical application may be an upper antenna and a lower antenna, each mounted on an aircraft. This type of dual antenna design allows the crew to direct the radio to the preferred antenna so as to increase coverage for the upper hemisphere or the lower hemisphere (or fore/aft, etc.) according to the operational requirements at that time. Such antenna switching is performed by switching the antenna control lines and the RF coaxial lines via a combination of coax switches and conventional control line switching usually performed by relays. The result is an effective communications system that provides a desired spatial coverage, but may frequently results in some interferences due to the practical limitations of space available to locate antennas.
As receiver-transmitters have become capable of covering a wider spectrum of frequencies, the design of the antenna hardware has become more complex and more expensive. Active impedance tuning elements in the antenna are digitally switched in or out of the antenna's internal impedance matching mechanisms to adjust the effective impedance of the antenna for optimum/efficient transmission.
Furthermore, as the capabilities of radios continue to increase, or as the number of radios installed on the airborne platform (eg; helicopter or fixed wing) increase, the potential for mutual interference increases. Close spacing of dedicated antennas can result in the radiated power of one radio interfering with another radio whose antenna is in proximity to the other antenna that is transmitting. The nature of the interference may be caused by transmit power of a level such that the receiving radio/antenna's receiver bandwidth processes the RF energy at the edges of its receiver bandwidth. This is sometimes referred to as the skirts of the receiver. This undesired interference problem is further increased when the radios are wideband units that cover a broad portion of the RF spectrum. When wideband transmitters of any kind are utilized such as for communications, navigation, IFF, etc., the harmonic content of each transmitter may also interfere with any of the receiving devices located in proximity.
Aircraft may typically have from three to as many as fifty antennas on the fuselage. Each antenna is installed to achieve proper coverage and the correct ground plane. The ability to locate an antenna at any arbitrary location to avoid interference may not be possible due to lack of ground plane, interference with maintenance access, or ground clearance. Interference of one transmitter with another receiver is most often a compromise to balance coverage, pattern efficiency, and mutual interference. As the number of antennas increases, so does the difficulty in locating antennas. These types of considerations must be addressed for ground stations, fixed wing aircraft, and helicopters.
Accordingly, it is desirable to provide a communication system which provides desired spatial coverage while minimizing interference due to the practical limitations associated with the space available to locate a multiple of antennas.